Uranium Health Effects

A discussion of chemical and radiological health effects associated with exposure to uranium and its compounds.

Chemical Toxicity

Exposure to uranium can result in both chemical and radiological toxicity. The main chemical effect associated with exposure to uranium and its compounds is kidney toxicity. This toxicity can be caused by breathing air containing uranium dusts or by eating substances containing uranium, which then enters the bloodstream. Once in the bloodstream, the uranium compounds are filtered by the kidneys, where they can cause damage to the kidney cells. Very high uranium intakes (ranging from about 50 to 150 mg depending on the individual) can cause acute kidney failure and death. At lower intake levels (around 25 to 40 mg), damage can be detected by the presence of protein and dead cells in the urine, but there are no other symptoms. Also, at lower intake levels, the kidney repairs itself over a period of several weeks after the uranium exposure has stopped.

Radiological Toxicity

Several possible health effects are associated with human exposure to radiation from uranium. Because all uranium isotopes mainly emit alpha particles that have little penetrating ability, the main radiation hazard from uranium occurs when uranium compounds are ingested or inhaled. However, workers in the vicinity of large quantities of uranium in storage or in a processing facility also are exposed to low levels of external radiation from uranium decay products. At the exposure levels typically associated with the handling and processing of uranium, the primary radiation health effect of concern is an increased probability of the exposed individual developing cancer during their lifetime. Cancer cases induced by radiation are generally indistinguishable from other "naturally occurring" cancers and occur years after the exposure takes place. The probability of developing a radiation-induced cancer increases with increasing uranium intakes.

Compound Solubility and Route of Exposure

The extent of damage from exposure to a uranium compound depends on the solubility of the compound and the route of exposure. In most assessments only inhalation, ingestion, and external radiation are considered. Although absorption of some soluble compounds through the skin is possible, such dermal exposures generally are not significant. For inhalation or ingestion of soluble or moderately soluble compounds such as uranyl fluoride (UO2F2) or uranium tetrafluoride (UF4), the uranium enters the bloodstream and reaches the kidney and other internal organs, so that chemical toxicity is of primary importance. For inhalation of insoluble compounds such as uranium dioxide (UO2) and triuranium octaoxide (U3O8), the uranium is generally deposited in the lungs and can remain there for long periods of time (months or years). The main concern from exposure to these insoluble compounds is increased cancer risk from the internal exposure to radioactivity. Ingested insoluble compounds are poorly absorbed from the gastrointestinal tract and are only retained in the body for a short time, thus generally having a low toxicity.

For more details on uranium health effects, see also Section 4.3.1 of the PEIS.